Flat field metallurgical microscope objective



o OR 3,399,017

Aug. 27, 1968 o. E. JUDD 3,399,017

I FLAT FIELD METALLURGICAL MICROSCOPE OBJECTIVE Filed Aug. 25. 1965OBJECTIVE MOUNTING s4 SHOULDER -R r IIIb 1 9 III a IlIo u 11b 6 II 1..R5

lIo

IO ll OBJECT PLANE DUANE E. JUDD INVENTOR.

adepwa,

ATTORNEY.

United States Patent York Filed Aug. 25, 1965, Ser. No. 482,444 2Claims. (Cl. 350-224) The present invention relates to an opticalobjective for use on metallographs and the like and more particularly itrelates to improvements therein.

Optical objectives of the kind generally described herebelow have beendisclosed in a copending application of Harold E. Rosenberger, Ser. No.408,875, filed Nov. 4, 1964, and having the same assignee, wherein isdescribed in particular a superior microscope objective for use withbiological specimens which are usually diascopically illuminated bytransmitted light. It has been discovered that when such an objective isused in metallurgical microscopes where the specimen has a specularsurface and is opaque, the image formed by specular light reflected fromthe specimen is degraded with respect to contrast of the critical imagefeatures by the simultaneous ghost reflections caused by the verticalilluminator at the air-glass lens surfaces in the objective.Furthermore, anti-reflection coating when applied to said air-glass lenssurfaces may reduce but does not eliminate the above-describeddifiiculty.

In view of the foregoing statements, it is an object of the presentinvention to provide a microscope semiobjective of the kind described inthe above-mentioned patent appplication having together with a 5Xcorrector lens substantially X overall magnification wherein ghostreflections from air-glass lens surfaces therein are reduced to aninnocuous condition.

It is a further object to provide such an objective having a very fiatfield and low distortion along with a superior degree of correction forastigmatism, coma and spherical image aberrations.

Further objects and advantages will be found in the arrangement anddetailed structure of the parts of said objective by reference to thefollowing specification and the accompanying drawing wherein the singlefigure is an optical diagram showing a preferred form of said invention.

The present microscope semi-objective per se is rated at 2Xmagnification and is designated in the drawing generally by the numeral10. It is a member of a group of related metallographic semi-objectiveshaving different magnification ratings which are interchangeably used incommon with a single negative form corrector lens of 5x magnification asdescribed in the aforementioned application of Rosenberger. Saidcorrector lens is designated by numeral in the drawing and itsmagnification rating of 5X, when combined with the 2X magnification ofthe present semi-objective, produces a total magnification of 10X forthe entire objective, and corrects certain aberrations in the imagingproperties of said semi-objective in the same manner as recited in citedpatent application. Corrector lens 20 is located on the optical axis 11of the semi-objective at a fixed distance 8 rearwardly from an objectiveshoulder 12.

According to the present invention, the form and arrangement of the lensmembers in said semi-objective as well as the constructional data, areso chosen as to achieve a fiat field and good correction for astigmatismand coma without the aforesaid ghost reflections.

The semi-objective 10 per se has a magnification of 2.0x and iscomprised of a front doublet lens designated I, an intermediate doubletlens designated II, and a rear doublet lens designated III, all of whichare optically aligned on optical axis 11. Doublet lens I is spaced at anaxial distance designated S rearwardly of the object plane of theobjective. Doublet lens II is spaced at an axial distance designated 8,from lens I and is followed by an axial space designated 8;, whichseparates lenses II and III.

Front doublet lens I comprises a front double convex lens element Inwhich lies in contact on its rear side with a double concave lenselement designated lb. The second doublet lens II comprises :a frontpositive meniscus lens element designated Ila and a negative meniscuslens element designated IIb contacting the rear side of element Ila. Inthe rearmost doublet lens III, the front lens element is designated 111aand is negative meniscus in form. Contacting the rear surface of lenselement IIIa is a rear double convex lens element designated IIIb.

The equivalent focal lengths F P and F of the successive doublet lensesI, II and III respectively have values as given in the table ofmathematical statements herebelow as stated in terms of P whichrepresents the equivalent focal length of the semi-objective 10 combinedwith the aforesaid 5 X negative corrector lens, said values beingpractical and effective in producing within the ranges stated objectiveshaving excellent performance characteristics.

The constructional data relating to the successive lens elements Ia toIIIb of said semi-objective 10 are given herebelow in terms of F, saiddata including the successive lens radii designated R to R wherein theminus sign is used with surfaces whose centers of curvature lie on theentrant side of the vertex thereof, said data further including theequivalent focal lengths P --F F11, -F -F1H5 and Fun, Of the SUCCBSSIVClens elements, and the successive axial thicknesses t, to r,respectively, as well as the successive air spaces 8,, S; and 8;,starting at the object plane, the minus sign used with the focal lengthvalues meaning negative focal length,

The lens elements Ia to IIIb are made from glass having the refractiveindex thereof designated by n (Ia) to n (IIIb) respectively and havingthe Abbe numbers desnated w(Ia) to v(IlIb) respectively, the absolutevalues thereof being given in the table of mathematical statementsherebelow,

1.7475(n (Ia) 1.7545 1.51 (n (Ib) (1.5170 1.51 l0(n (IIa) (1.51701.7l66(n (IIb) (1.7234 l.6856(n IIIa) (1.6924 1.5379(n (IIIb) (1.544127.74(v(Ia) (27.86 69.86(v(Ib) (70.14 69.86(v(IIa) (7O. 14 29.24(v(llb)(29.36 30.84(v(IIla) (30.96 59.78(v(IIIb) (60.02

More specifically, the values of the constructional data for onesuccessful form of the present invention are given substantially interms of F in the table herebelow wherein the meaning of the symbolismremains the same as found hereabove,

The corresponding absolute values of the Abbe numbers I and refractiveindex ru of the glass in said lens elements Ia to IIIb are givensubstantially in the table herebelow,

v(la):=='27. 8 v(Ib) =70.0 u(IIa) =70.0 r(IIb)-.=29.3 v(IIIa) =30.9v(IIIb)=59.9 n Ua) 1.751 n AIb)'= 1.514 n ((IIa)=1.514 n (IIb)== 1.720 n(IIIa)= 1.689 n (IIIb)= 1.54 1

' "From the foregoing description, it will be appreciated that there ishere provided a semi-objective which is part of a compound objectivehaving a corrector lens whereby the field is flattened to a superiordegree and wherein all monochromatic image aberrations have been wellcorrected in accordance with the objects of the present invention.

Although only a single form of the invention has been shown anddescribed in'detail, other forms are possible and changes may be madeinthe details of construction within the limits claimed withoutdeparting from the spirit of the invention as defined in the claims hereappended.

I claim: v

1. A microscope semi-objective having a combined positive power of'lOxwhen used with a rearwardly aligned negative corrector lens of 5Xmagnification, said semi-objective comprising a front doublet lensdesignated I consisting of a front double convex element designated Iaand a rear double concave element designated Ib in contact therewith,said front doublet lens having an equivalent focal length which isdesignated F said front doublet lens I being located at an axialdistance S rearwardly from the object plane of said objective,

a second doublet lens designated H consisting of a front positivemeniscus element designated Ila and a rear negative meniscus elementdesignated IIb in contact therewith, said second doublet lens beingspaced rearwardly of lens I at an axial distance designated S, andhaving an equivalent focal length designated F and a third doublet lensdesignated III consisting of a front negative meniscus elementdesignated IIIa and a rear double convex element designated IIIb lyingin contact therewith, said third lens III being spaced from lens H at anaxial distance designated 8;, and having an equivalent focal lengthdesignated F the specific values for the constructional data for saidsemi-objective being given substantially herebelow for the equivalentfocal lengths F to F the successive axial thicknesses of the successivelens elements being designated t to t and the aforesaid air spaceswherein F designates the equivalent focal length of the semi-objectiveand corrector lens together, and further characterized by the refractiveindices n (Ia), n (Ib), n (IIa), n (IIb), n (IIIa), n (IIIb)respectively of the successive lens elements Ia to IIIb, and A'bbenumbers of the glasses from which said elements are formed beingdesignated v(Ia), v(Ib), v(IIa), v(IIb), w(IIIa), v(IIIb) respectively,the specific absolute values thereof being given substantially in thetable of mathematical statements here- 6 I 2. A microscope objectivehaving a combined positive R =.903F t =.2740F power of x when used witha rearw-ardly aligned nega- -R =.480F t =.2117F tive corrector lens of5x magnification, said semiobjec- R =.557F t =.l110F tive comprising -R=3.530F t =.1580F a front doublet lens designated I consisting of afront 5 R =.373F t =.1975F double convex element designated la and arear -R =.632F S =.1580F double concave element designated lb in contactR =1.l23F S =.6070F therewith, R =.599F S =.1054F said front doubletlens I being located at an axial dis- R =1.775F S =.3499F tance Srearwardly from the object plane of said 10 =.1054F objective,

a second doublet lens designated II consisting of a front positivemeniscus element designated Ila and a rear negative element designated11b in contact therewith,

and further characterized by the successive lens elements Ia to IIIbbeing formed from glass aving refractive indices n (Ia) to n (IIIb)respectively, and

said second doublet being spaced rearwardly of lens 15 Abbi: numbeirs(Ia) to (lnh).respectlvely have I at an axi a1 distance S2 and specificabsolute values as given substantially in the a third doublet lensdesignated III consisting of a front table of values herebelow negativemeniscus element designated 111a and a rear n (Ia) 1.75l (Ia)-=27.8

double convex element designated IIIb lying in conn (Ib)=1.5 14 (lb)=70.0

tact therewith, said third lens III being spaced from (IIa)=1.514(IIa)'=70.0

lens II at an axial distance designated 8; and being (1Ib)=1 720(1Ib)=29,3

spaced from said negative corrector lens by an axial (11I -1 689 (IIIa)30 9 distance designated S n (IIIb) 1.541 (IIIb) =59.9 the axialthicknesses of said elements successively from the front beingdesignated t to i and the successive References Cited lens surfacesbeing designated R to R numbering from the front, wherein the minus signused UNITED STATES PATENTS with the R values denotes that the center ofcurvature 2,153,202 5/1939 Schade.

of such surface is located on the object side of its 3,113,964 1/ 1964lawa- FOR ENT the specific values of the constructional data R to R EIGNT I S t to 1 and S to S being given in terms of F which 945467 1/1964Great Bntamrepresent the equivalent focal length of said semiobjectiveandcorrector lens together in the table of DAVID SCHONBERG' pr'maryExamme" mathematical statements herebelow, R, J. STERN, AssistantExaminer.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,399,017 August 27, 1968 Duane E Judd It is certified that errorappears in the above identified patent and that said Letters Patent arehereby corrected as shown below:

Co1umn 2,-1ine'59-,' "'3'.'5494F" shou1d'read'- 3.45941 Signed andsealed this 10th day of March 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. Attesting Officer WILLIAM E. SCHUYLER, IR.

Commissioner of Patents

1. A MICROSCOPE SEMI-OBJECTIVE HAVING A COMBINED POSITIVE POWER OF 10XWHEN USED WITH MAGNIFICATION, SAID ALIGNED NEGATIVE CORRECTOR LENS OF 5XMAGNIFICATION, SAID SEMI-OBJECTIVE COMPRISING A FRONT DOUBLET LENSDESIGNATED I CONSISTING OF A FRONT DOUBLE CONVEX ELEMENT DESIGNATED IAAND A REAR DOUBLE CONCAVE ELEMENT DESIGNATED IB IN CONTACT THEREWITH,SAID FRONT DOUBLET LENS HAVING AN EQUIVALENT FOCAL LENGTH WHICH ISDESIGNATED F1, SAID FRONT DOUBLET LENS I BEING LOCATED AT AN AXIALDISTANCE S1 REARWARDLY FROM THE OBJECT PLANE OF SAID OBJECTIVE, A SECONDDOUBLET LENS DESIGNATED II CONSISTING OF A FRONT POSITIVE MENISCUSELEMENT DESIGNATED IIA AND A REAR NEGATIVE MENISCUS ELEMENT DESIGNATEDIIB IN CONTACT THEREWITH, SAID SECOND DOUBLET LENS BEING SPACEDREARWARDLY OF LENS I AT AN AXIAL DISTANCE DESIGNATED S2 AND HAVING ANEQUIVALENT FOCAL LENGTH DESIGNATED FII, AND A THIRD DOUBLET LENSDESIGNATED III CONSISTING OF A FRONT NEGATIVE MENISCUS ELEMENTDESIGNATED IIIA AND A REAR DOUBLE CONVEX ELEMENT DESIGNATED IIIB LYINGIN CONTACT THEREWITH, SAID THIRD LENS III BEING SPACED FROM LENS II ATAN AXIAL DISTANCE DESIGNATED S3 AND HAVING AN EQUIVALENT FOCAL LENGTHDESIGNATED FIII,